Biogenic emission inventory development: field assessment of the GAP vegetation database in California

Abstract

Given the key role played by biogenic volatile organic compounds (BVOC) in tropospheric chemistry and regional air quality, it is critical to generate accurate BVOC emission inventories. Indeed, formulating effective air quality attainment strategies for formation of ozone, fine particles, and other secondary air pollutants may depend in some regions upon the strength of biogenic emissions, requiring the geolocated characterization of plant species and their areal coverages. Vegetation databases developed through remote sensing methods require calibration and validation from ground-based measurements to be reliably used for BVOC modeling. A recent GIS-based description of vegetation coverage in the natural areas of the US is provided by the Gap Analysis Program (GAP) database. We conducted an assessment of this database in central California through quantitative ground-based vegetation surveys in 18 polygons, using a modified stratified randomized sampling design, to evaluate the use of GAP for developing BVOC emission inventories. The plant species listed by GAP accounted for between 0% and 88% of the relative cover in the polygons, with a mean of 43%. Of the 76 species listed by GAP for which data were collected, 33 were found to be correctly listed within their respective assemblages, 13 were found to be listed for the wrong assemblage, and 30 were below percentages of co-dominants of any assemblage. Summed over all 18 polygons, BVOC emission indices based on field data were 20% less than those based on GAP, but for individual polygons differences ranged from −100% to more than +100%.